1. Field of the Invention
This application relates to Japanese Patent Application No. 2007-039667, filed Feb. 20, 2007. The disclosure of the aforementioned application is hereby incorporated by reference in its entirety.
The present invention relates to a process for producing a semiconductor device, and an adhesive sheet used in the process.
2. Background Art
In order to meet the request that semiconductor devices are made finer and caused to have higher functions, the wiring width of power supply lines arranged in the entire area of the main faces of their semiconductor chips (semiconductor elements) or the interval between signal lines arranged therein has been becoming narrower. For this reason, the impedance thereof increases or signals between signal lines of different nodes interfere with each other so as to cause hindrance to the exhibition of sufficient performances for the operation speed of the semiconductor chips, the margin of the operating voltage thereof, the resistance thereof against damage by electrostatic discharge, and others. In order to solve these problems, for example, in Japanese Unexamined Patent Publication S55-111151 and Japanese Unexamined Patent Publication 2002-261233, package structures wherein semiconductor elements are laminated are suggested.
As a material used to stick semiconductor elements to a substrate or the like, the following examples are suggested: an example wherein a thermosetting paste resin is used (see, for example, Japanese Unexamined Patent Publication 2002-179769); and examples wherein an adhesive sheet composed of a thermoplastic resin and a thermosetting resin is used (see, for example, Japanese Unexamined Patent Publication 2002-261233 and Japanese Unexamined Patent Publication 2000-104040).
In conventional processes for producing a semiconductor device, an adhesive sheet or an adhesive is used to cause a semiconductor element to adhere onto a substrate, a lead frame or a semiconductor element. The adhesion is attained by attaching the semiconductor element to the substrate or the like under pressure (die attachment), and then curing the adhesive sheet or the like through a heating step. Furthermore, wire bonding is performed to connect the semiconductor element electrically to the substrate. Thereafter, molding is conducted by use of a sealing resin, and then the resin is after-cured to attain sealing with the sealing resin.
However, when the wire bonding is performed, the semiconductor element on the substrate or the like is moved by ultrasonic vibration or heating. It is therefore necessary to conduct a heating step before the wire bonding to heat and cure the existing thermosetting paste resin or thermosetting adhesive sheet, thereby bonding the semiconductor element so as not to be moved.
About an adhesive sheet made of a thermosetting resin, or an adhesive sheet made of both of a thermosetting resin and a thermoplastic resin, a heating step is further required to keep the adhering strength certainly between the sheet and an adherend and to improve the wettability therebetween after the sheet undergoes die attachment and before the sheet undergoes wire bonding.
However, when the adhesive sheet or the like is heated before the wire bonding, there is caused a problem that a volatile gas is generated from the adhesive sheet or the like. The volatile gas contaminates the existing bonding pads. Thus, it becomes impossible to perform the wire bonding in many cases.
When the adhesive sheet or the like is heated and cured, curing shrinkage or the like is also generated in the adhesive sheet or the like. Following this, a stress is generated to cause a problem that the lead frame or substrate (as well as the semiconductor element) is warped. Additionally, in the wire bonding step, the stress results in a problem that the semiconductor element is cracked. As semiconductor elements have been becoming thinner and smaller in recent years, the thickness of the semiconductor elements has been becoming smaller so as to change from about 200 μm, which is a conventional thickness, to a value below the conventional thickness, or a value 100 μm or less. Considering the present situation, the problems that a substrate or the like is warped and a semiconductor element thereon is cracked become more serious. Thus, a solution against the problems has become more important.